American or native razor clams in north Norfolk?
There are many records of razor clams (jacknife clams) in iNaturalist from the north Norfolk coast, but the identity of these is somewhat confused. Often huge quantities of razor clams are washed up on beaches, but it is unclear whether these are the native ‘pod razor’ (Ensis siliqua) or the American jacknife clam Ensis leei (otherwise known as Ensis directus or Ensis americanus).
Apparently, Ensis leei was first identified in 1989 on Holme beach, Norfolk (Howlett 1990). It is native to the Atlantic coast of North America and is thought to have been introduced via mainland Europe where the species has been established in the German Elbe Estuary and Dutch Wadden Sea since 1979 (https://archimer.ifremer.fr/doc/00586/69820/67710.pdf). In the United Kingdom, it was reported as one of the most common living bivalves on the shore in 1995 (Ovcharenko et al., 2009). At present, E. leei is known to occur all along the eastern coast of the United Kingdom, from the Humber and the Wash to the eastern coast of Kent.
In 1997, an experimental fishery using water-jet dredges was carried out by local fishermen in the Wash and North Norfolk and this showed that catches consisted almost entirely of the introduced razorfish Ensis leei/directus, rather than the two native species Ensis siliqua and E. arcuatus. Scientific surveys were carried out by the Centre for Environment, Fisheries and Aquaculture Science (CEFAS) in 1999 and 2003. E. directus was found to inhabit a wide range of substrates from almost pure mud on the banks of channels within The Wash, to clean sand on the North Norfolk coast (https://www.cefas.co.uk/publications/shellfishnews/shellnews16.pdf).
I have unknowingly reported both species in iNaturalist over the years, but I suspect they should all be listed as Ensis leei/directus.
[Ovcharenko, I., Olenin, S., and Gollasch, S. 2009. Chapter 13: Species accounts of 100 of the most invasive alien species in Europe. Ensis americanus (Gould), American jack knife clam (Solenidae, Mollusca), p. 288. In Handbook of Alien Species in Europe. Invading Nature. Springer Series in Invasion Ecology, Vol. 3. Ed. by DAISIE. Springer Science + Business Media B.V. 400 pp.]
Observations
Photos / Sounds
What
Atlantic Jackknife (Ensis leei)Observer
heliastes21Description
See my journal entry about this non-native species: https://www.inaturalist.org/journal/heliastes21/60443-american-or-native-razor-clams-in-north-norfolk
Comments
Almost all Ensis, which I collected in 1991 and following years along the Dutch coast, were what was then known as Ensis directus or E. americanus (now E. leei). Already in those years, you could find them in huge quantities washed up on the beach, especially on the Dutch Wadden Islands, after a storm - sometimes, locally, in greater quantities than all other bivalves combined. I only encountered the native Ensis ensis occasionally, as a subfossil shell. I did find Ensis siliqua sometimes. They are somewhat hard to tell apart, and the ID guides usually did not include the American species. My supervisors at Natural History Museum, Leiden (now Naturalis) told me the difference - you have to look at the hinge and whether the corners are diagonal or not. I think this was the first time that I realised, how dominant an invasive species can be - I was really quite intrigued by it!
(I remember them mainly from the North Sea side of the Dutch Wadden Isles - not so much from the Wadden Sea side)
Add a Comment